1. Field of the Invention
The present invention relates to a method of correcting a mask pattern for obtaining a desired photoresist pattern that corresponds to a design pattern by optical lithography with a mask pattern.
2. Description of the Related Art
Making a semiconductor device includes a lithography process. The lithography process is a process to pattern a resist using a projection optical system type exposure system. The exposure system for patterning is equipped with a mask pattern called “reticle”, and performs patterning on a resist with an image formed by transmission of light irradiated to the mask pattern.
When patterning is performed by the above-described exposure system with the mask pattern, and if the exposure system is used at the edge of its capability, the pattern shape obtained by the exposure becomes different from that of the design pattern.
To solve this problem, so-called “Optical proximity Correction” is employed, by which correction is made on the mask pattern so as to obtain a pattern shape similar to the design pattern.
The Optical Proximity Correction is described below with an example when patterning is performed by two exposures using a phase-shifting mask. The design pattern 10 is shown in FIG. 2. The phase-shifting mask and a Cr trim mask, which are used for patterning a resist to obtain the design pattern, are shown in FIGS. 3 and 4, respectively. The resist pattern 20 obtained by patterning by exposure while overlaying those masks is shown in FIG. 5.
The design pattern 10 has a shape, in which one rectangle is imposed between two wider rectangles. When patterning is simply performed with such pattern shape, the obtained resist pattern has rounded corners as shown in FIG. 5, and the width between the positions a′and b′ in FIG. 5 which corresponds to the width between the positions a and b in FIG. 2 becomes larger than the width between the positions a and b.
The above-described phase-shifting mask 30 is Comprised of a Cr light-shielding section 31, 0° phase-shifter 32 and 180° phase shifter 33, which are included in the Cr light-shielding section 31. In the phase-shifting mask 30 shown in FIG. 3, the line defined by apex 34 and apex 35 is referred to as an edge 35, which is a line that can define the design pattern 10, resist pattern 20 or the like, in addition to the phase-shifting mask 30.
The optical proximity correction method is a method wherein a correction is made to a edge of the phase-shifting mask 30 in FIG. 3 and an edge of the Cr trim mask 40 in advance so as to make the image transferred by exposure more similar to the design pattern 10. More specifically, since the distance between the positions a′ and b′ in FIG. 5 tends to be made larger, the edge shape of the mask patterns such as phase-shifting mask 30 and Cr trim mask 40, which correspond to the positions a and b that correspond to the positions a′ and b′, are corrected.
The above-described mask pattern correcting method by the optical proximity correction is described in the patent references 1-3.
According to the patent reference 1 (JP2001-17497), in order to perform optical proximity correction, a mask pattern is modeled, light intensity distribution is simulated, and then correction is made to the mask pattern.
According to the patent reference 2 (JP12-162758), optical proximity correction is performed by first sorting the mask patterns, and then performing optical proximity correction to the sorted mask patterns.
According to the patent reference 3 (JP11-218899), a mask pattern is corrected by marking the circumference of the mask pattern with evaluation points, and then correcting the mask pattern with the evaluation points.
In the above-described methods, in order to obtain a desired mask pattern, the mask pattern is corrected by determining the intensity distribution of accumulated energy of light as two-dimensional light intensity distribution, and then repeating simulations based on the two-dimensional light intensity distribution.
In the above methods, the two-dimensional light intensity distribution, i.e. the intensity distribution of accumulated energy, needs to be determined in the whole mask pattern area. Thus, if many calculations of the two-dimensional light intensity distribution are required, it will take more time to correct the mask pattern, which deteriorates the work efficiency.